This invention relates to an internal combustion engine and more particularly to an improved variable valve timing mechanism and control arrangement for such engines.
In order to improve the performance of an internal combustion engine and particularly those that are required to run over wide varieties of loads and speeds, such as is typical with automotive applications, it has been proposed to employ variable valve timing mechanisms (VVT). These VVT mechanisms are effective to change the timing of the events of opening and closing of the valves of the engine. They may be employed to either or both the intake and exhaust valves. By doing this, it is possible to change the valve timing in such a way so as to obtain optimum timing for a wider range of running variations.
Although various types of mechanisms have been employed for this purpose, those most commonly used normally employ a connection between a camshaft drive element and the camshaft which, when actuated, varies the phase angle between the camshaft drive element and the camshaft. Quite often, these devices are operated by hydraulic pressure.
The use of hydraulic pressure for operating the variable valve timing mechanism has a number of advantages. One of these advantages is that it permits the use of the lubricating system for the engine as a source of hydraulic pressure for operating the variable valve timing mechanism.
Generally, the mechanism includes a hydraulic supply line and a hydraulic return line which communicate with the engine lubricating system. A movable valve element controls the communication of these supply and return lines with the hydraulic actuator for the VVT mechanism. Thus, there are a fair number of components which must be employed in order to achieve the desired operation. Obviously, these mechanisms must be fairly accurate and also quite compact.
Normally, the camshaft is mounted directly in an engine body by journal surfaces formed in that engine body. The engine body is frequently but not always a cylinder head of the engine. Thus, it has been the practice to provide the engine body with supply and return lines and also a passage in which the controlling valve element can be mounted. This obviously gives rise to the necessity of machining the engine body in order to form these passages as well as the passage for the valve element.
It is, of course, possible to mount the valve element in the supply lines externally of the engine body, but this then complicates the overall engine construction and gives rise to the potential for leakage and misfit. However, to perform the necessary machining operations on the engine body itself can be quite complicated.
It is, therefore, a principal object of this invention to provide an improved and simplified arrangement for mounting a camshaft and for supplying fluid to a variable valve timing mechanism for the camshaft wherein a number of hydraulic passages and valve supporting passage are formed in a separate body that is detachably connected in a precise manner to the engine body.
It is also a principal object of this invention to provide an improved, simplified and easily machined variable valve timing actuating mechanism for an internal combustion engine.
From the foregoing description, it should be readily apparent that most hydraulically operated variable valve timing mechanisms utilize a valve element that is slidably supported in a body of the engine for controlling the operation of the variable valve timing mechanism. These valve elements are normally operated by means of a controlling element such as an electric servo motor or electric solenoid. This presents an additional problem in how the solenoid is mounted on the engine body.
Normally, the valve element that controls the flow of hydraulic fluid to and from the variable valve element reciprocates along an axis that is parallel to the axis of rotation of the camshaft. The actuating solenoid is, therefore, mounted on an external body of the engine and has a reciprocal axis that extends also parallel to the camshaft axis.
This, however, presents some spatial problems as will be best understood by reference to FIG. 1. This view is an enlarged, partial cross-sectional view showing a variable valve timing mechanism of the type utilized in prior art engines.
As may be seen, the engine includes a cylinder head 11. This cylinder head 11 supports a plurality of valves (not shown) that control the flow of gasses into and out of the engine combustion chambers. The cylinder head 11 has at one end thereof a bearing surface 12 that receives a bearing surface 13 of a cam shaft 14. The cam shaft 14 has a plurality of lobes (not shown) for operating the engine valves in any suitable manner.
A bearing cap 15 is detachably connected to the cylinder head 11 by fasteners 16 and completes the journaling of the camshaft 14 for rotation about a generally longitudinally extending axis that is parallel to the axis of rotation of the crankshaft of the engine. This crankshaft is not shown in FIG. 1.
However, the crankshaft has a driving timing sprocket that drives a chain 17 which is entrained around a driven timing sprocket 18 that is associated with the camshaft 14. A variable valve timing mechanism, indicated generally by the reference numeral 19, connects the driven sprocket 18 to the camshaft 14 so as to establish a driving relationship therebetween. This driving relationship is via a helical spline so that axial movement of a spline element will change the phase angle between the sprocket 18 and the camshaft 14. This causes variations in the valve timing, as is well known in this art.
The bearing surface 12 of the cylinder head 11 is formed by an upstanding boss 21 in which a hydraulic pressure line 23 is formed, which hydraulic pressure line is in communication with a high pressure pump for the engine lubricating system. This line 23 serves, among other things, to deliver lubricant to the bearing surface 12, the bearing surface 13 of the camshaft 14 and a corresponding bearing surface 24 of the bearing cap 15. These passages are formed adjacent a fastener 25 which is among the various fasteners employed to affix the cylinder head 11 to the cylinder block of the engine.
The pressure line 23 also communicates with a valve element, indicated generally by the reference numeral 26 that is slidably supported in a bore 27 formed in the cylinder head portion 22 and which controls the flow of fluid to and from a supply conduit 28 and a return conduit 29 that are associated with a control element (not shown) of the variable valve timing mechanism 19 for changing the aforenoted phase angle.
A solenoid motor 31 is affixed to the forward end of the cylinder head 11 and is coupled to the valve spool 26 for operating it. This solenoid 31 is operated by means of an ECU in accordance with any desired control strategy. This strategy is based primarily on engine speed and load.
As may be seen, the solenoid 31, because of its forwardly extending mounting, takes up space between the drive sprocket 18 and chain 17 and requires the variable valve timing mechanism 19 to be disposed at a substantially cantilevered distance L' from the threaded fastener 25. This also extends a substantial distance forwardly of the cylinder head so as to make the overall engine construction rather bulky.
It is, therefore, a still further object of this invention to provide an improved control arrangement for the variable valve timing mechanism of an internal combustion engine that permits a more compact construction.
It is a further object of this invention to provide a hydraulic control for a variable valve timing mechanism wherein an actuating solenoid for the valve element and/or the valve element itself can be positioned in a location that does not require extension of the camshaft drive mechanism and the variable valve timing mechanism from the journaled surface of the camshaft with which it is associated.